How to get phone calls working on builds higher than 18363.

You will need:
- An image, a backup, or a Windows 10 Mobile/Desktop installation of build 18363 or lower with the SIM already inserted in the past and confirmed working with calls.
- regedit.exe

We will consider the system with calls working (ie a build less or equal to 18363) as the "Working System" here.
The builds higher than 18363 will be considered as the "Target System" here.

On the Working System, confirm that calls are working.
Access the registry of the Working System via regedit (for Desktop, just open regedit, for Windows 10 Mobile, use mass storage to load the SOFTWARE hive offline on your computer).

In the SOFTWARE hive of the Working System, go to the following location:
Microsoft\Windows NT\CurrentVersion\Notifications\Data

You will need to export the following value: 0D8A0B2EA3BDF475 (for SIM 1), 0D8A0B2EA3BDFC75 (for SIM 2 if applicable).

On the Target System, open regedit, import the value you exported earlier from the Working System and add the following registry value to prevent reprovisioning:

SOFTWARE\OEM\RILINITSVC
DisableCallReg=dword:00000001

Reboot the device and you should have calls working.

Note: This guide will not make texts working.
The values you exported are unique to your own sim but do not seem to bind to any identifier present on the sim that can be read physically or programmatically hence why this process is not automated yet.